Abstract

We report the design of a laser wakefield accelerator (LWA) with external injection by a rf photogun and acceleration by a linear wakefield in a capillary discharge channel. The design process is complex due to the large number of intricately coupled free parameters. To alleviate this problem, we performed front-to-end simulations of the complete system. The tool we used was the general particle-tracking code, extended with a module representing the linear wakefield by a two-dimensional traveling wave with appropriate wavelength and amplitude. Given the limitations of existing technology for the longest discharge plasma wavelength and shortest electron bunch length , we studied the regime in which the wakefield acts as slicer and buncher, while rejecting a large fraction of the injected bunch. The optimized parameters for the injected bunch are , at , to be injected into a long channel at a plasma density of . A linear wakefield is generated by a laser focused to . The simulations predict an accelerated output of , bunches at , with energy spread below 10%. The design is currently being implemented. The design process also led to an important conclusion: output specifications directly comparable to those reported recently from “laser-into-gas jet” experiments are feasible, provided the performance of the rf photogun is considerably enhanced. The paper outlines a photogun design providing such a performance level.

Received 02 January 2006Accepted 13 March 2006Published online 01 June 2006

Acknowledgments:

This research was funded by the Technology Foundation STW, Applied Science Division of NWO and the technology program of the Ministry of Economic Affairs, the Royal Netherlands Academy for Arts and Sciences (KNAW), and the Foundation for Fundamental Research on Matter (FOM).

Article outline:I. INTRODUCTIONII. THE SIMULATION TOOLA. Injector and beam transport lineB. Modeling the plasma channel for LWAIII. APPLICATION TO THE TRUE DESIGNA. General considerations and layout of the injector systemB. Constraints and free parameters for the laser wakefield acceleratorIV. RESULTS OF ITERATIVE OPTIMIZATION OF THE LASER WAKEFIELD ACCELERATORV. OUTLOOKVI. CONCLUSIONS